This invention generally relates to analysis of urine for particles and sediments of various types. Examples include leukocytes, erythrocytes, epithelial cells, oval fat bodies, hyaline casts, granular casts, leukocytes casts, renal cell casts, waxy casts, fatty casts, uric acid crystals, calcium oxalate crystals, hippuric acid crystals, calcium phosphate crystals, triple phosphate crystals and the like. Such analyses are useful for determining whether a patient requires medical attention.
At present, urine sediment analysis may be done through manual microscopy, flow cytometry, flow cell imaging, and microfluidic slide imaging. Of these, microfluidic slide imaging has advantages over the others. Manual microscopy is accurate, but labor intensive and requires trained technicians. Flow cytometry and flow cell imaging are less accurate, although they require less manual labor. However, follow up with manual microscopy if often required. Examples of flow cell imaging and flow cytometry may be found in U.S. Pat. No. 6,825,926 and U.S. Pat. No. 3,826,364, respectively.
U.S. Pat. No. 5,699,794 discusses many other patents in the field and discloses an automated system and a cell used in urine sediment analysis. U.S. Pat. No. 3,777,283 discloses a plastic slide in which capillary force is used to draw a liquid specimen into a transparent viewing chamber. U.S. Pat. No. 4,441,793 discloses a slide for microscopic evaluation having one or two openings for introduction of a sample by a pipette into a viewing area. However, the slide does not separate the viewing chamber from the sample entry opening, which makes it more difficult to accurately read the images in a microscope. Another example of manual microscopy in a slide may be found in U.S. Pat. No. 6,004,821, where several types of analyses are carried out in a single sample-containing slide. In one analysis type, a portion of the urine sample is sent to a chamber for identifying urine casts. The chamber includes a water absorbent layer (e.g. a hydrogel) that removes the water from the sample, fixing the casts for visual inspection. In another type of analysis, bacteria and red and white blood cells are segregated and can be seen in a formed particle chamber having variable depth.
Analysis employing microfluidic techniques has become prominent in recent years for use with various biological samples, including urine and blood. In general, microfluidic disks or similar “chips” generally provide a group of interconnected chambers through which a fluid sample is passed to encounter various reagents. The reactions of the sample with the reagents provide information (e.g. color changes and the like) which can be related to the presence of analytes in the sample. In a typical microfluidic device, the chambers and interconnecting passageways are formed in a base layer, often a plastic material, and a cover is placed over the base. For an example, see U.S. Pat. No. 7,094,354. Such microfluidic devices can be adapted to visual analysis of urine samples for sediments. However, the cost of fabricating such microfluidic devices is rather high and less expensive designs would be desirable. The present inventors have found a less expensive, but still accurate method of analysis for urine sediments and other particles.
The '354 patent teaches the separation of particles in a microfluidic device, particularly the separation of red blood cells from a whole blood sample, with the use of low centrifugal force. Such separations were contrasted with the high centrifugal force used in bulk blood separation. An elongated chamber was used to allow accumulation of red blood cells at the bottom, while the separated plasma was withdrawn from the top of the chamber. The chamber's wall surfaces were made to have a surface energy matching or slightly lower than that of the red blood cells. The combination of the appropriate wall surface energy and capillary forces made possible the separation of red blood cells without using high centrifugal force.
If particles are to be identified in urine samples and studied, they should be relatively stationary. One means of positioning particles is shown in the '821 patent mentioned above, that is, by absorbing water from the sample the particles are immobilized. The '821 patent also shows the use of an angled chamber that apparently sorts the particles by their sizes. In the present invention, the particles and sediments are separated and immobilized by providing a viewing chamber having the appropriate surface energy, as will be discussed in more detail below.